1. Field of the Invention
The present invention relates to a fluoroboron compound or a salt thereof from which a cyclic ether fused with an aromatic ring can be formed by an intramolecular alkoxymethylation reaction, a production method thereof, and a method for synthesizing a compound having a cyclic ether-fused aromatic ring using the fluoroboron compound or the salt thereof.
2. Description of the Related Art
To date, there have been reports on intermolecular coupling reactions in which an oxymethyl group, such as an alkoxymethyl group or a hydroxymethyl group, is introduced in an aromatic ring by the use of an organotin compound, such as an alkoxymethyl tin compound, in the presence of a palladium catalyst. As the organotin compounds which can be used in this reaction, methoxymethyltributyltin disclosed in Non-patent Document 1, hydroxymethyltributyltin disclosed in Non-patent Document 2, and the like have been reported. In addition, an alkoxymethylfluoroboron compound is disclosed in Non-patent Documents 3 and 4.    [Non-patent Document 1] Chem. Lett., 1225, 1984.    [Non-patent Document 2] Chem. Lett., 997, 1985.    [Non-patent Document 3] Org. Lett., 8, 2031, 2006.    [Non-patent Document 4] Org. Lett., 8, 2767, 2006.
The organotin compounds disclosed in the abovementioned Non-patent Documents 1 and 2 are known as reagents that can alkoxymethylate or hydroxymethylate (hereinafter these processes are collectively referred to as “oxymethylation”) the aromatic ring in the presence of a metal catalyst. However, the toxicity of these organotin compounds may cause problems, and thus they are not suited for industrial use. Moreover, the organotin compounds are not suited for large industrial scale production since the production requires purification by chromatography using silica gel in many cases. For this reason, the development of compounds to be used in the metal catalyzed oxymethylation reaction of aromatic rings which are excellent in terms of safety and which can also be easily produced on a large scale and the establishment of a method for producing such compounds have been desired. Organoboron compounds are highly safe as compared to organotin compounds. Moreover, it is known that the organic fluoroboron compounds generally have excellent stability and are also easy to handle. However, there is no known example of using the oxymethyl fluoroboron compounds disclosed in the abovementioned Non-patent Documents 3 and 4 for the intermolecular oxymethylation of aromatic rings.
Furthermore, in addition to the abovementioned problems, the alkoxymethylation reaction described above is limited to the intermolecular reaction, and no method is known to date for synthesizing a compound having a cyclic ether-fused aromatic ring by the intramolecular alkoxymethylation reaction in the presence of a metal catalyst.